1. Field of the Invention
The present invention relates generally to methods and systems for production of hydrocarbons and/or other products from various subsurface formations such as hydrocarbon containing formations.
2. Description of Related Art
Hydrocarbons obtained from subterranean formations are often used as energy resources, as feedstocks, and as consumer products. Concerns over depletion of available hydrocarbon resources and concerns over declining overall quality of produced hydrocarbons have led to development of processes for recovery that is more efficient, processing and/or use of available hydrocarbon resources. In-situ processes may be used to remove hydrocarbon materials from subterranean formations that were previously inaccessible and/or too expensive to extract using available methods.
Substantial reserves of hydrocarbons exist in formations that have relatively low permeability. Examples of such formations include the Eagle Ford shale, the Barnett shale, the Travis Peak and Cotton Valley formations and the Bakken shale. Several methods have been proposed and/or used for producing heavy hydrocarbons from relatively low permeability formations. Recovery of hydrocarbons from low permeability subterranean formations is difficult because of the low mobility of fluids in the pore space in the subterranean formation (ultra-low permeability rocks). This makes the production and injection of fluids from such reservoirs very difficult. Similar problems are encountered in heavy oil reservoirs (reservoirs containing crude oil with a viscosity larger than about 100 centipoise). Mobility of the fluids in heavy oil reservoirs is small, and thus, injecting and producing from such hydrocarbon bearing rock is difficult.
U.S. Pat. No. 5,289,881 to Schuh describes a horizontal well completion apparatus and method for heavy, viscous oil in a producing zone using a single well. Hot injection fluid is injected into an injection string, reduced to a lower pressure by passing the injection fluid through a choke. A packer separates the upper well annulus from the lower well annulus. Insulation surrounds injection tubing string between the packer and the wellhead. Perforations in the horizontal portion of the well allow heated oil to flow into the lower annulus in the horizontal portion of the well where is picked up by the injected fluid and lifted to the surface of the well by a jet pump. The temperature and pressure of the injection fluid, and the pumping rate of the produced fluids control temperature and pressure in the lower well annulus.
Oil recovery by primary production (hydrocarbon production accomplished using the natural energy in the reservoir) is usually very low for unconventional oil and gas reservoirs. In unconventional reservoirs such as the Bakken and Eagle Ford formations, typical primary production is about 5% of the original oil in place compared to 15 to 25% in permeable subterranean formations. Thus, a very large resource of hydrocarbons is left unrecovered.
In conventional (high permeability) reservoirs, water injection and enhanced oil recovery methods such as CO2 flooding and chemical injection are used to recover additional hydrocarbons. The use of these methods is restricted by the inability to inject at sufficiently high rates into low permeability or heavy oil reservoirs. During injection processes, the injection pressures is limited as the subterranean formation will fracture once the fracture gradient of the rock is exceeded. Since the injection pressure and/or rate is limited, injection of fluids takes time and may have little to no impact on hydrocarbon production. For example, in a chemical flooding process, a minimum of 0.25 times the hydrocarbon pore volume of the reservoir area being flooded may be required to see any incremental oil recovery. In low permeability formations, achieving this may take many decades (or at least many years).
Although, there has been a significant amount of effort to develop methods and systems to produce hydrocarbons and/or other products from relatively low permeability formations, there is still a need for improved methods and systems for production of hydrocarbons.